Abstract
The migration of extensive social groups towards specific spawning grounds in vast and diverse ocean environments is an integral part of the regular spawning process of many oceanic fish species. Oceanic fish in such migrations typically seek locations with environmental parameters that maximize the probability of successful spawning and egg/larval survival. The 3D spatio-temporal dynamics of these behavioral processes are largely unknown due to technical difficulties in sensing the ocean environment over wide areas. Here, we use ocean acoustic waveguide remote sensing (OAWRS) to instantaneously image immense herring groups over continental-shelf-scale areas at the Georges Bank spawning ground. Via multi-spectral OAWRS measurements, we capture a shift in swimbladder resonance peak correlated with the herring groups’ up-slope spawning migration, enabling 3D spatial behavioral dynamics to be instantaneously inferred over thousands of square kilometers. We show that herring groups maintain near-bottom vertical distributions with negative buoyancy throughout the migration. We find a spatial correlation greater than 0.9 between the average herring group depth and corresponding seafloor depth for migratory paths along the bathymetric gradient. This is consistent with herring groups maintaining near-seafloor paths to both search for optimal spawning conditions and reduce the risk of predator attacks during the migration to shallower waters where near-surface predators are more dangerous. This analysis shows that multi-spectral resonance sensing with OAWRS can be used as an effective tool to instantaneously image and continuously monitor the behavioral dynamics of swimbladder-bearing fish group behavior in three spatial dimensions over continental-shelf scales.
Highlights
During their reproductive period, oceanic fish of many species migrate to specific grounds to spawn, where they form extensive social groups for cooperative reproduction that often span hundreds to thousands of square kilometers [1,2,3]
We measure the spatial variation in the frequency response of scattering from large herring groups during an upslope migration towards the Georges Bank spawning ground via multi-spectral resonance sensing with ocean acoustic waveguide remote sensing (OAWRS) (Figure 3)
Multi-spectral resonance sensing with ocean acoustic waveguide remote sensing (OAWRS) is an effective tool to instantaneously image and continuously monitor the 3D group behavioral dynamics of swimbladder-bearing fish in natural habitats over continental-shelf scales
Summary
Oceanic fish of many species migrate to specific grounds to spawn, where they form extensive social groups for cooperative reproduction that often span hundreds to thousands of square kilometers [1,2,3]. The 3D spatial behavioral dynamics of these immense social groups are largely unknown due to difficulties in sensing over such wide areas, but hold important clues about the ability of their respective species to survive. The 3D spatial behavioral dynamics of large Atlantic herring groups are inferred via multi-spectral resonance sensing with OAWRS. Herring group parameters are estimated via an exhaustive search for an empirical best-fit between the measured and modeled frequency responses at each spatial position. Assuming an approximately uniform vertical layer of herring [1,4,5], the group parameters estimated here include mean shoal depth, shoal thickness, neutral buoyancy depth, and areal population density
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